The following “dangerous” file extensions are blocked and are not allowed to be sent or received through our email services. These extensions are also blocked within zip, rar and other types of compressed archives. We disallow these extensions as they are commonly used in viruses, malware, rootkits, ransomware and other security issues. Attempting to send an email containing an attachment with a blocked extension will result in the email being rejected and sent back to you with a notice. If you are sent an email containing an attachment with a blocked extension, the email will also be rejected.

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@Richard – Thank you for your feedback. The list is based on attachments that we have seen and tested over 6 months for malicious content, .xlsm files were not something we saw regularly or with any malicious content.